Motor or engine mount from mixtures of elastomers and halogenated polymers

ABSTRACT

Vulcanized rubber parts suitable to dampen vibrations generated by mechanical devices are disclosed. The parts are based on a cured composition comprising one or a mixture of a diolefin polymers, e.g., natural rubber, a halogenated copolymer of a C 4  to C 7  isomonoolefin, e.g., isobutylene, and a para-alkylstyrene, filler and a curing system. The vulcanized parts exhibit improved aging and high temperature resistance and reduced deterioration of dynamic properties after long term exposure to high temperatures.

CROSS REFERENCE TO RELATED APPLICATION

This application was filed as a Provisional Application, U.S. Ser. No.:60/002,365, filed Aug. 15, 1995.

TECHNICAL FIELD

The present invention relates to vulcanized rubber parts useful todampen and/or isolate vibrations generated by mechanical devices.

BACKGROUND

Machines such as automobile, truck or jet engines, compressors andindustrial air conditioners, automotive exhaust systems and like dynamicdevices generate significant vibration during operation. This vibrationwill be transmitted directly to support structures with which thedynamic devices is mounted or associated, e.g., an automobile oraircraft frame, a compressor frame, or a floor or rooftop. In order tominimize transfer of vibration from the operating dynamic device to theassociated support structure, i.e., isolate the vibrations, it is commonto interpose vibration damping and/or isolation means between thedynamic device and the associated support structure. Examples of suchvibration damping and/or isolation means would be vibration-absorbing,elastomeric automobile or truck engine mounts placed between thebrackets which are used to bolt the engine to the associated auto ortruck frame, exhaust hangers, pads interposed between an air conditioneror compressor and a frame or floor and the like.

Vibration damping and/or isolation materials known in the art includevulcanized shapes, e.g., squares, rectangles or cylindrical shapesprepared from vulcanized rubber. These dampening and/or isolationdevices can be solid rubber, foamed rubber or solid rubber enclosing afluid-containing cavity. Suitable rubbers which have heretofore beenused in such applications include halogenated and non-halogenated butylrubber (copolymer of isobutylene with up to 10 wt % isoprene), naturalrubber and synthetic elastomeric polymers and copolymers of butadiene.

In addition, EPA 0533746 discloses vibration damping materials based ona vulcanized mixture containing a halogenated copolymer of a C₄ to C₇isomonoolefin and para-alkystyrene, carbon black, a plasticizer oil anda curing system.

Although natural rubber is an elastomer of choice in some applicationsbecause of its superior dynamic properties, i.e., good tensile, modulusand spring rate (stress/strain) properties, the aging and hightemperature resistance of cured parts based on natural rubbervulcanizates are poor, thereby limiting the effective life of suchparts. For example, engine mounts associated with modem engines must beable to withstand temperatures as high as 150° C. for periods in therange of 1,000 to 5,000 hours without significant loss of dynamicproperties, in order to meet current and anticipated automotivestandards.

SUMMARY

The present invention provides shaped rubber parts, either solid,foamed, or fluid filled useful to isolating vibrations and dampeningvibrations generated by mechanical devices. More particularly, theinvention provides mechanical devices comprising a dynamic means whichgenerates heat and/or vibrations, e.g., an automotive engine, anelectric motor, and a static structure which supports said dynamicmeans, e.g., an automotive frame, and which is connected to said dynamicmeans, e.g., by bolting together brackets attached to the frame andengine, and having a vulcanized rubber vibration, isolation, and/ordamping part interposed between said dynamic means and said staticstructure at said point of connection, e.g., one or more disc-shapedrubber parts sandwiched between the engine and frame brackets. Theimprovement provided by the invention comprises the utilization as saidrubber part of a shaped, vulcanized composition comprising a mixture of:

1. An elastomeric olefin polymer or copolymer;

2. an elastomeric, halogen-containing copolymer of a C₄ to C₇isomonoolefin and a para-alkylstyrene, said halogen-containing copolymercomprising from 10 to 35 wt % of the elastomer content of the mixture;

3. a particulate filler; and

4. a curing system for said composition.

The elastomeric olefin polymer or copolymer can be derived frommonoolefins or diolefins. Molded or shaped parts prepared from thevulcanized composition exhibit both excellent isolation and vibrationdamping properties at high and low temperatures and enhanced heat agingresistance, thereby rendering them particularly suitable forapplications involving prolonged exposure to high temperatures.

DESCRIPTION

The halogen-containing elastomer present in the curable composition ofthis invention is a chlorinated or brominated interpolymer of a C₄ to C₇isomonolefin and a para-alkylstyrene.

Halogenated interpolymers based on a C₄ to C₇ isomonoolefin, such asisobutylene, and a para-alkylstryrene, such as para-methylstyrene, areknown in the art as evidenced by U.S. Pat. No. 5,162,445, the completedisclosure of which is incorporated herein by reference.

Preferred materials are the halogenation product of a random copolymerof a C₄ to C₇ isomonoolefin, such as isobutylene, and apara-alkylstyrene comonomer wherein at least some of the alkylsubstituent groups present in the styrene monomer units contain halogen.Preferred materials may be characterized as isobutylene interpolymerscontaining the following monomer units randomly spaced along the polymerchains: ##STR1## wherein at least about 5% of the comonomer unitspresent in the polymer chain are of the structure of formula 2, R and R'are independently hydrogen or C₁ to C₄ alkyl, R" is independentlyhydrogen, C₁ to C₄ alkyl or X, and X is bromine or chlorine, and whereinthe interpolymer is otherwise substantially free of any halogen in thepolymer backbone chain.

With reference isobutylene as the isoolefin comonomer, theseinterpolymers are inclusive of:

1. copolymers consisting of isobutylene and a monomer having thestructure of formula 2 wherein R" is hydrogen or C₁ to C₄ alkyl, eg,copolymers of isobutylene and a monohalo-substituted para-alkylstyrene;

2. terpolymers comprising isobutylene and a mixture of monomers havingthe structure of formulas 1 and 2 wherein R" is hydrogen or C₁ to C₄alkyl, eg, terpolymers of isobutylene, a para-alkylstyrene and amonohalo-substituted para-alkylstyrene;

3. terpolymers comprising isobutylene and a mixture of monomers havingthe structure of formula 2 wherein, with respect to a major proportionof the formula 2 monomer, R" is hydrogen or C₁ to C₄ alkyl and, withrespect to a minor proportion of said formula 2 monomer, R" is bromineor chlorine, eg, terpolymers of isobutylene, a mono-halo substitutedpara-alkylstyrene and a di-halo substituted para-alkylstyrene; and

4. tetrapolymers comprising isobutylene and a mixture of monomers havingthe structure of formulas 1 and 2 wherein, with respect to majorproportion of the formula 2 monomer, R" is hydrogen or C₁ to C₄ alkyland, with respect to a minor proportion of said formula 2 monomer, R" isbromine or chlorine, eg, tetrapolymers of isobutylene, apara-alkylstyrene, a monohalo-substituted para-alkylstyrene and adihalo-substituted para-alkylstyrene.

As stated above, these halogenated interpolymers are prepared using acopolymer of a C₄ to C₇ isoolefin and a para-alkylstyrene as thehalogenation substrate. Interpolymers having the composition (a), (b),(c) or (d) above will be produced as a function of the severity of thehalogenation reaction. For example, mild halogenation will tend to yieldinterpolymers of the characteristics of (b), stronger halogenation willyield interpolymers of the characteristics of (a) or (d) and thestrongest halogenation will yield terpolymers having the characteristicsof (c).

The most preferred elastomers used in the compositions of the presentinvention are random elastomeric brominated terpolymers comprisingisobutylene and para-methylstyrene (PMS) containing from about 0.5 toabout 20 wt % PMS, more preferably from about 2 to about 15 wt % PMS,wherein up to about 65% of the PMS monomer units contain amono-bromomethyl group. These elastomeric copolymers generally exhibit anumber average molecular weight in the range of from about 50,000 toabout 250,000, more preferably from about 80,000 to about 180,000. Fromabout 5 up to about 65% of the total PMS monomer content of theterpolymer contains a mono-bromomethyl group with essentially nobromination occurring in the polymer backbone or in the aromatic ring.The bromine content of these terpolymers generally ranges from about 0.1to about 5 mole %.

The major elastomeric component of the composition of the inventioncomprises a olefin polymer or copolymer. Preferred diolefin polymers arepolymers of conjugated dienes such as natural rubber, syntheticpolyisoprene, polybutadiene, elastomeric terpolymers of ethylene,propylene and a non-conjugated diene (EPDM rubber) as well aselastomeric copolymers of butadiene with up to about 35 wt % styreneand/or acrylonitrile, as well as mixtures of two or more of theseelastomers. The preferred diolefin polymer is natural rubber becausecured natural rubber exhibits superior vibration dampening and dynamicphysical properties. Preferred monoolefin copolymers are ethylenemonoolefin copolymers wherein the monoolefin has from 3 to 16 carbonatoms, preferably 3-8 carbon atoms, most preferably 3 or 4 carbon atoms.

The content of the halogen-containing polymer is such that it comprisesfrom about 10 to 35 wt % of the total elastomer content of thecomposition, more preferably from about 15 to 30 wt % of the totalelastomer content of the composition.

Suitable curing systems include curing agents such as sulfur andmixtures of sulfur with sulfur-containing accelerators such as thiuramsulfides, dithiocarbamates, thioureas, thiazoles, sulfanamides,quanidines and like materials. The curing agent may also comprise aresin cure such as phenolic resins, brominated phenolic resins and thelike. The quantity of such curing agents added to the composition willgenerally range from about 1 to 6 phr, more preferably from about 1.5 to4 phr.

Preferred curatives comprise a mixture of sulfur and an accelerator suchas benzothiazyl disulfide, N-oxydiethylene benzothiazole-2-sulfonamide,2-mercaptobenzothiazole, alkyl phenol disulfides, tetramethylthiuramdisulfide, m-phenylenebismaleimide, N,N¹ -diarylguanidines, and likeknown materials.

The sulfur curing system is preferably used as a cocurative in curingsystems also containing zinc oxide or an equivalent thereof, e.g., zincchloride, zinc bromide or ferric chloride, as a cocuring agent. Zincoxide is normally used in such systems at a level of from about 0.2 toabout 7 parts by weight per 100 parts by weight of elastomer. Thepresent invention provides for particularly good low cure reversionwhere zinc oxide is present at relatively low levels in the range offrom about 0.5 to about 3.5 parts by weight per 100 parts by weight ofelastomer.

The vulcanizable composition may also contain other conventionaladditives known in the art, including fillers such as carbon black orsilica, stabilizers, antioxidants, plasticizers, processing oils,pigments, flame retardants, and like additives as is known in the art.

Examples of fillers include inorganic fillers such as carbon black,silica, calcium carbonate, talc, clay and metal powder, and organicfillers such as high-styrene resin, coumarone-indene resin, phenolicresin, lignin, modified melamine resins and petroleum resins. Thepreferred filler is reinforcing grade carbon black present at a level offrom about 10 to 65 parts by weight per hundred parts by weight of totalelastomer content of the blend, more preferably from about 20 to 60parts by weight.

Examples of lubricants include petroleum-type lubricants such as oils,paraffins, and liquid paraffins, coal tar-type lubricants such as coaltar and coal tar pitch; fatty oil-type lubricants such as beeswax,carnauba wax and lanolin; fatty acids and fatty acid salts such aslicinoleic acid, palmitic acid, barium stearate, calcium stearate andzinc laureate; and synthetic polymeric substances such as petroleumresins.

Suitable plasticizer oils include paraffinic, aromatic or naphthenicpetroleum oils as are known in the art. These may be present in thecomposition at a level of from 0 to about 20% by weight of thecomposition, more preferably from about 1 to 10% by weight of thecomposition.

The composition of the present invention may comprise a total mixedelastomer content in an amount ranging from about 40 to 80, preferablyfrom about 55 to about 65 weight percent, the carbon black in an amountranging from about 10 to about 30, preferably from about 20 to about 25weight percent; the plasticizer oil in an amount ranging from above 0 toabout 20, preferably from about 1 to about 10 weight percent; the totalamount of other fillers and additives in an amount ranging from above 0to about 10, preferably from about 3 to about 5 weight percent; and thecuring agent in an amount ranging from about 1 to 5, preferably fromabout 1 to 2 weight percent, all said percentages being based on theweight of the total composition.

The vulcanizable composition may be prepared and blended using anysuitable mixing device such as a two-roll mill, an internal mixer(Brabender Plasticorder), a Banbury Mixer, a kneader or a similar mixingdevice. Blending temperatures and times may range about 100° C. to 180°C. and from about 1 to 10 minutes respectively. The sequence of mixing,time of mixing and temperatures employed are such that a uniformdispersion of all components of the composition, except the curatives,is first achieved.

A useful mixing procedure utilizes a Banbury mixer in which theelastomeric polymers, the filler and a process oil are added and thecomposition mixed for the desired time or to a particular temperature toachieve adequate dispersion of the ingredients. Alternatively, therubber and a portion of the filler (e.g., one-third to two-thirds) ismixed for a short time (e.g., about 1 to 3 minutes) followed by theremainder of the filler and oil. Mixing is continued for about 5 to 10minutes at high rotor speed during which time the mixed compound reachesa preferred temperature of about 160° C. Following cooling, the compoundis mixed with curatives in a second step to disperse the curatives atrelatively low temperature, e.g., about 80 to about 120° C. Variationsin mixing will be readily apparent to those skilled in the art and thepresent invention is not limited by the mixing procedure. The mixing isperformed to disperse all components of the composition thoroughly anduniformly.

Vulcanization of a molded article, for example a motor mount, may becarried out in heated presses under conditions well known to thoseskilled in the art. It is preferred that vulcanization be effected attemperatures of about 140 to about 250° C. and for periods of about 2 toabout 60 minutes. Curing time will be affected by the thickness of thearticle and the concentration and type of curing agent as well as theinitial halogen content of the halogenated polymer. However, thevulcanization parameters can readily be established with a fewexperiments utilizing e.g., a laboratory characterization device wellknown in the art, the Monsanto Oscillating Disc Cure Rheometer(described in detail in American Society for Testing and Materials,Standard ASTM D 2084).

Alternatively, the curable composition can be injection molded to formshaped articles and held in the mold for a sufficient time to form acured, shaped article.

The composition of the present invention may be used in producingvibration damping and/or isolation parts used to isolate or decrease theeffect of vibrations from motor, engines and the like. It isparticularly suitable for use in the production of elastomeric mountingsfor control of vibration, for example automotive body and engine mounts;automotive exhaust hangers; dynamic absorbers (e.g., shock absorbers);bushings; automotive suspension bumpers, and the like. The compositionsare especially useful in the assembly of automotive engine mounts whichare subjected to high operating temperatures of up to about 150° C. Insuch an application, molded parts in the shape of discs are interposedbetween motor and auto frame brackets prior to bolting the bracketstogether to secure the motor to the frame. For especially high-qualityisolation use of hydromounts, i.e., rubber enclosing a fluid, isdesirable. The enclosed liquids are generally high boiling. Typically,the liquids are selected from glycols such as ethylene glycol andpropylene glycol.

The following examples are illustrative of the invention. The materialsused in preparing the various formulations as abbreviated in the Tableswere as follows:

    __________________________________________________________________________    MDX 90-10            Random brominated copolymer of isobutylene and para-methylstyrene            2            containing about 7.5% wt of para-methylstyrene, 2.0 wt % bromine            (1.2            mole %), 0.07 calcium (as calcium stearate), 0.04 wt % phenolic            antioxidant and having a Mooney Viscosity ML (1 + 8) at            125° to 45 + 5.    SMR-5   Natural rubber (standard Malaysian rubber, Grade #5)    SUNPAR ®2280            Paraffic processing oil.    Aroma 790            Aromatic processing oil.    CBS     N-cyclohexyl-2-benzothiazylsufenamide    Vultac #5            Alkyl phenol disuffide (Pennewalt Corp.)    __________________________________________________________________________

EXAMPLES 1-3

A series of formulations described in Table 1 were prepared bycompounding the elastomers, fillers and other additives shown in Table 1in a laboratory Banbury mixer. The mixtures were heated from atemperature of 80° C. up to 160° C. over a period of about 6 minutes,after which the master batch compositions were dumped from the mixer.

Portions of this master batch were then formulated with a curativemixture of sulfur vulcanization accelerators and the other curatives asshown in Table 1A by adding the curative mixture to the rubber stock andmilling the mixture on a two roll mill at 50° C. for about 7 minutes.

The curable mixtures were evaluated for vulcanization activity accordingto ASTM D-2084 using a Monsanto Oscillating Disc Rheometer and thenphysical properties of the vulcanizates were evaluated by vulcanizingtest pads under the various cure conditions set forth in Table 2 usingstandard ASTM laboratory test practice as follows:

Mooney Viscosity--ASTM D-1646

Mooney Scorch--ASTM D-1646

Tensile Properties--ASTM D-3182 through D-3192

Tensile Properties--ASTM D-412

Ozone Resistance--ASTM D-3395-86 (Method A)

* Covers mixing conditions and curing

** Covers tension testing and tensile properties.

                  TABLE 1    ______________________________________             Example             1        2          3             PHR  G.      PHR     G.    PHR  G.    ______________________________________    SMR        100    710     80    592   70   532    EMDX90-10  0      0       20    148   30   228    CARBON BLACK               55     390.5   55    409   55   418    SUNPAR 2280               0      0       5     37    5    38    AROMA 790  5      35.5    0     0     0    0    STEARIC ACID               2      14.2    0.5   3.7   0.5  3.8    PARAFFIN WAX               1.0    7.2     0     0     0    0    ANTIOXIDANT               2      14.2    0     0     0    0    ZnO        5      35.5    0     0     0    0    TOTAL      170    1207    160.5 1167.7                                          160.5                                               1219.8    ______________________________________

                  TABLE 1A    ______________________________________    CURATIVES PHR)                  Ex. 1       Ex. 2  Ex. 3    ______________________________________    ZnO (PHR)     0           2      2    CBS (PHR)     0.7         2      2    SULFUR (PHR)  3.5         0.5    0.5    VULTAC #5 (PHR)                  0           1.5    1.5    ______________________________________

Physical property data for the cured formulations is shown in Table 2.

                  TABLE 2    ______________________________________    Compound No.      1        2        3    ______________________________________    Mooney Vis., ML 1 + 4 100° C.                      24.4     39.3     44.3    Mooney Scorch             5 pt. min.   20.5     9.9    8.4    125° C., ML             35 pt min.   23.3     30.5   32.5             Min. Reading 15.9     29.2   33.8    Rheometer, Arc +/- 30    160° C.           ML lb.inch     3.3      6.4    7.5           MH lb.inch     80.7     69.5   71.4           T52 m.s        1.6      2.8    2.3           Tc90 m.s       6.2      5.9    6.5    Original           Cure Time Min. 7        6      7    Cured  Hardness Shore A                          63       59     62    160° C.           100% Modulus, Kg/cm.sup.2                          28       23     26           300% Modulus, Kg/cm.sup.2                          134      121    127           Tensile Strength, Kg/cm.sup.2                          235      204    195           % Elongation   490      460    450           Tear Strength, Kg/cm                          48       43     33    Aged   Cure Time Min.    125° C.           Hardness, Shore A                          78       48     52    72 hrs.           100% Modulus, Kg/cm.sup.2                          --       13     18           300% Modulus, Kg/cm.sup.2                          --       --     --           Tensile Strength, Kg/cm.sup.2                          38       28     37           % Elongation   <50      200    190           Tear Strength, Kg/cm                          12       8      8    ______________________________________    Test Items        1        2        3    ______________________________________    Compression Set    100° C. 22 hrs. 25%                      52.4     38.6     38.3    -20° C. 22 hrs 25%                      16.5     62.5     51.0    Rebound -Zwick    -20° C.    13.1     10.8     8.7    0° C.      38.5     23.3     17.1    30° C.     65.6     49.4     43.1    60° C.     72.9     65.0     62.8    Low Temp brittleness Point    Calculated Value (° C.)                      -58.6    -61.0    -60.8    Ozone Test    Static, 40° C. for 24 hours    50 pphm. 20% extension.                      A-2      B-5      NC    100 pphm. 50% extension                      C-5      C-5      B-5    Dynamic, 20% ex.    50 pphm. 40° C. for 48 hrs.                      B-2      B-5      NC    ______________________________________

Dynamic properties of the cured formulations of Examples 1-3 wereevaluated at 24° C. after storage at 150° C. over periods of timeranging from 0 to 210 hours. The effect of aging on such properties aselastic spring rate (K'--N/mm), damping coefficient (C-N-Sec/mm) andtangent delta (a measure of damping efficiency) at frequencies of 15,100 and 200 Hz are shown in Table 3.

The data in Table 3 show a marked decrease in the change of K', C andTan Delta properties associated with the formulations of Examples 2 and3 over an aging period of 0 to 210 hours as compared with the Example 1formulation which contains natural rubber as the sole elastomer. This isindicative of an enhancement of the heat aging properties of the naturalrubber and a reduction of the rate of deterioration of the normally gooddynamic properties of natural rubber.

                                      TABLE 3    __________________________________________________________________________             AGING EFFECT                       AGING EFFECT                                 AGING EFFECT    HOURS    ON K'     ON C      ON TAN, DELTA    AT 150° C.          Hz EX. 1                2   3  EX. 1                          2   3  EX. 1                                    2   3    __________________________________________________________________________    0     15 840                730 802                       0.95                          1.3 1.6                                 0.11                                    0.16                                        0.19    70    15 953                812 854                       1.51                          1.5 1.8                                 0.15                                    0.18                                        0.20    140   15 1159                964 1010                       2.26                          2.0 2.2                                 0.18                                    0.19                                        0.20    210   15 1097                964 1052                       2.32                          2.0 2.4                                 0.20                                    0.20                                        0.21    0     100             1108                1063                    1210                       0.17                          0.36                              0.52                                 0.10                                    0.21                                        0.27    70    100             1315                1191                    1284                       0.33                          0.45                              0.57                                 0.16                                    0.23                                        0.28    140   100             1738                1466                    1538                       0.47                          0.54                              0.66                                 0.17                                    0.23                                        0.27    210   100             1836                1558                    1744                       0.50                          0.56                              0.71                                 0.17                                    0.22                                        0.26    0     200             1223                1228                    1370                       0.12                          0.25                              0.36                                 0.12                                    0.26                                        0.33    70    200             1423                1361                    1488                       0.21                          0.31                              0.41                                 0.18                                    0.29                                        0.34    140   200             1865                1635                    1737                       0.28                          0.36                              0.44                                 0.19                                    0.27                                        0.32    210   200             2002                1745                    1983                       0.32                          0.37                              0.48                                 0.20                                    0.27                                        0.30    __________________________________________________________________________

We claim:
 1. A motor or engine mount comprising a mixture of:a) naturalrubber, b) an elastomeric brominated copolymer of isobutylene andpara-methy styrene, said copolymer containing up to 20 wt % ofpara-methylstyrene, said bromine-containing copolymer comprising fromabout 10 to 35 wt % of the elastomer content of the mixture; c) aparticulate filler, and d) a curing system.
 2. The mount of claim 1wherein said mount is solid.
 3. The mount of claim 1 wherein said mountis fluid containing.
 4. The mount of claim 1 wherein said mount isfoamed.
 5. In a mechanical device comprising an automotive engine whichgenerates heat and/or vibrations and an automotive frame which supportssaid automotive engine and which is connected to said automotive engineand having a vulcanized rubber part interposed between said automotiveengine and said automotive frame at their point of connection, themovement comprising the utilization as said rubber part a shapedvulcanized composition comprising a mixture of:a. natural rubber, b. anelastomeric brominated copolymer of isobutylene and para-methylstyrene,said copolymer containing up to 20 wt % of para-methylstyrene, c. aparticulate filler, and d. a curing system.